Substituted benzimidazoles are substituted sulfoxides which are potent inhibitors of gastric acid secretion. Such substituted sulfoxides are described for example in EP 0005129. These compounds are susceptible to degradation and/or transformation in both acid and neutral media. The acidic decomposition of these acid labile compounds is due to an acid catalyzed reaction described by G. Rackur et al., in Biochem. Biophys. Res. Commun. 1985: 128(1). P477-484.
In order to provide a pharmaceutical composition containing such acid labile substances which is not degraded in the gastrointestinal tract, the acid labile substances must be enteric coated. However, pharmaceutically acceptable enteric coating materials are acidic in nature or contain acid reacting groups. Therefore, if the acid labile substances are directly covered by these enteric coating materials, the acid labile substance rapidly degrades.
U.S. Pat. Nos. 4,853,230 and 4,786,505 describe enteric coated pharmaceutical formulations of acid labile substances for oral use, where the cores contain acid labile drugs mixed with alkaline reacting substances. This is then coated with a first separating layer which is rapidly disintegrated in gastric fluid and a final enteric layer. However, the alkaline reacting substances in the core do not completely protect the acid labile substances from degradation and thus additional pH buffering substances are required. These formulations may also contain aluminium, potassium, sodium, calcium and magnesium which compounds or composites may be of concern for oral ingestion in humans.
U.S. Pat. No. 2,540,979 describes an enteric coated pharmaceutical in an oral dosage form, where the enteric coating is combined with a second and/or first coating of a water insoluble "wax" layer. This coating is not suitable as direct contact with acid labile substances as it will result in degradation of the acid labile active.
WO No. 85/03436 discloses a pharmaceutical preparation in which the core contains active drugs mixed with buffering compounds such as sodium dihydrogenphosphate which maintains a constant pH. A coating material is used to provide a constant rate of diffusion of the pharmaceutical active. However, this formulation is not suitable for acid labile compounds where a rapid release in the small intestine is required. The direct application of an enteric coating onto the pharmaceutical active would adversely influence the storage stability of the acid labile compounds contained therein.
DE-A1-1 204 363 describes a three layer coating method for pharmaceuticals. The first coating layer is a surface membrane soluble in gastric but insoluble in intestinal juice. The second coating layer is soluble at all physiological pHs and the third coating layer is an enteric coating. This method is complicated and is also not suitable for acid labile compounds such as substituted benzimidazoles where rapid release of the drug in the small intestine is required, as it results in a dosage form which is not dissolved in gastric juice and dissolves slowly in the small intestine.
There was therefore a need to develop a pharmaceutical composition for acid labile substances that adequately protected the acid labile active prior to its being release in the small intestine. Accordingly, a novel pharmaceutical composition was developed for the delivery of acid labile substances to the gut which differs from known compositions and delivery mechanisms in the type of stabilizer(s) utilized, the mechanism(s) of stabilization used in the core containing the acid labile compound(s), by the type of protector coat applied to the core(s), the mechanism(s) by which the protector coat elicits it's protective action and the type of enteric coating compound(s) used in the composition. These lead to a different mechanism by which the acid labile drug is released in the small intestine to provide a stabilized acid labile compound composition.